I have imported a class diagrams from RSA. All associations ends up "Bi-Directional" (Connector property "Direction) but I want them to be "Unspecified". It is possible to carry out the change association by association but is it possible to carry out the change for all association at one time?

Well no worries. The context for a script in EA includes a global variable Repository, so you can just create a script and call Repository.Execute() with a SQL statement and it'll do it. That method is undocumented, which is for a reason: it will bypass a lot of the stuff EA normally does to make sure the database stays consistent. In other words, it is quite possible to break a project beyond repair.

Note that while the snippet I posted should work (haven't tested it), it will change the direction of every single connector in the project. You did say "all". So either you'll have to narrow that statement down, or run the script in a temp project that only contains the stuff you want to modify.

I'm guessing that even in a temp project not all your connectors will be associations, so perhaps this would be more appropriate: